The present invention relates to a voltage monitoring apparatus for monitoring the voltage of a multiple-set battery, and in particular relates to a technique for avoiding power consumption when a failure has occurred in the voltage monitoring apparatus.
For example, a hybrid vehicle is provided with a high voltage battery as a power source for driving a motor. The high voltage battery obtains a high voltage by series connection of a plurality of unit cells of a secondary battery (storage battery) such as a nickel-hydrogen battery or a lithium battery, for example.
Further, since it is necessary to check the charging condition for each unit cell so that the secondary battery will not enter an overdischarge state or a overcharge state, a plurality of unit cells (e.g., 55 unit cells) have conventionally been divided into, for example, five blocks (each consisting of eleven unit cells) so as to measure, in real time, voltages outputted from the unit cells of each block using a voltage detection IC provided for each block, thereby determining whether or not the measured voltage of each unit cell falls within a given range.
Moreover, when the high voltage battery has been used for a long period of time while being charged and discharged repeatedly, or when the high voltage battery has been left unused for a long period of time, remaining capacities of power of the respective unit cells might be nonuniform. In such a case, the capacity of the high voltage battery to be used will be reduced, and sufficient power cannot be obtained from the high voltage battery. To cope with this, as described in Japanese Unexamined Patent Application Publication No. 2003-189490 (Patent Document 1), for example, an attempt has been made to uniformize remaining capacities of respective unit cells.
In a method for uniformizing remaining capacities described in Patent Document 1, the output voltage of each unit cell is detected when an ignition is OFF to detect the unit cell having the lowest output voltage, and the output voltages of the other unit cells are adjusted so that the output voltages of the other unit cells each become equal to the output voltage of the unit cell having the lowest output voltage, thereby uniformizing the remaining capacities of all the unit cells.
[Patent Document 1] JP-A-2003-189490
As described above, in the conventional example disclosed in Patent Document 1, a process for uniformizing the remaining capacities of the respective unit cells is executed when the ignition is OFF; therefore, while the ignition is OFF, it is necessary to operate a voltage detection circuit for detecting the output voltages of the respective unit cells, and a voltage adjustment circuit for adjusting the output voltages. These circuits are operated upon supply of power from an active power source.
In this conventional example, when an abnormality of some kind has occurred in the voltage detection circuit or the voltage adjustment circuit and the detection of the output voltages of the unit cells is disabled, or when the voltage adjustment circuit has become unable to perform the process for uniformizing the remaining capacities, the active power source continuously supplies power to the voltage detection circuit or the voltage adjustment circuit in which an abnormality has occurred. If this state is continued for a long time, there arises a problem that an abnormality occurs in a high voltage battery.
The present invention has been made to solve the above-described conventional problems, and its object is to provide a voltage monitoring apparatus for a multiple-set battery, which is capable of avoiding power consumption by disconnecting supply of power from an active power source upon occurrence of an abnormality of some kind in a voltage monitoring circuit for uniformizing output voltages of respective unit cells.